The disclosure relates generally to distributed antenna systems (DAS) and more particularly to techniques for minimizing downlink and uplink ripples within the DAS.
Wireless customers are increasingly demanding digital data services, such as streaming video signals. At the same time, some wireless customers use their wireless communication devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of DASs. DASs include remote antenna units (RAUs) configured to receive and transmit communications signals to client devices within the antenna range of the RAUs. DASs can be particularly useful when deployed inside buildings or other indoor environments where the wireless communication devices may not otherwise be able to effectively receive radio frequency (RF) signals from a source.
In this regard, FIG. 1 illustrates distribution of communications services to remote coverage areas 100(1)-100(N) of a DAS 102, wherein ‘N’ is the number of remote coverage areas. These communications services can include cellular services, wireless services, such as RF identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local area network (LAN), and wireless LAN (WLAN), wireless solutions (Bluetooth, Wi-Fi Global Positioning System (GPS) signal-based, and others) for location-based services, and combinations thereof, as examples. The remote coverage areas 100(1)-100(N) may be remotely located. In this regard, the remote coverage areas 100(1)-100(N) are created by and centered on RAUs 104(1)-104(N) connected to a head-end equipment (HEE) 106 (e.g., a head-end controller, a head-end unit, or a central unit). The HEE 106 may be communicatively coupled to a signal source 108, for example, a base transceiver station (BTS) or a baseband unit (BBU). In this regard, the HEE 106 receives downlink communications signals 110D from the signal source 108 to be distributed to the RAUs 104(1)-104(N). The RAUs 104(1)-104(N) are configured to receive the downlink communications signals 110D from the HEE 106 over a communications medium 112 to be distributed to the respective remote coverage areas 100(1)-100(N) of the RAUs 104(1)-104(N). In a non-limiting example, the communications medium 112 may be a wired communications medium, a wireless communications medium, or an optical fiber-based communications medium. Each of the RAUs 104(1)-104(N) may include an RF transmitter/receiver (not shown) and a respective antenna 114(1)-114(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 116 within the respective remote coverage areas 100(1)-100(N). The RAUs 104(1)-104(N) are also configured to receive uplink communications signals 110U from the client devices 116 in the respective remote coverage areas 100(1)-100(N) to be distributed to the signal source 108. The size of each of the remote coverage areas 100(1)-100(N) is determined by amount of RF power transmitted by the respective RAUs 104(1)-104(N), receiver sensitivity, antenna gain, and RF environment, as well as by RF transmitter/receiver sensitivity of the client devices 116. The client devices 116 usually have a fixed maximum RF receiver sensitivity, so that the above-mentioned properties of the RAUs 104(1)-104(N) mainly determine the size of the respective remote coverage areas 100(1)-100(N).
With reference to FIG. 1, the DAS 102 may be configured to support a wide range of frequency bands. For example, the downlink communications signals 110D are communicated in a downlink frequency band that ranges from one thousand nine hundred thirty megahertz (1930 MHz) to one thousand nine hundred ninety-five megahertz (1995 MHz). The uplink communications signals 110U are communicated in an uplink frequency band that ranges from one thousand eight hundred fifty megahertz (1850 MHz) to one thousand nine hundred fifteen megahertz (1915 MHz). To minimize out-of-band emissions, downlink and uplink bandpass filters (e.g., Chebyshev filter) (not shown) are commonly employed in the HEE 106 to pass the downlink communications signals 110D and the uplink communications signals 110U in the 1930-1995 MHz downlink frequency band and the 1850-1915 MHz uplink frequency band, respectively. Due to the inherent non-linearity, the downlink and uplink bandpass filters can generate periodic insertion losses with frequency (also known as ripples) in the downlink communications signals 110D and the uplink communications signals 110U. Since excessive ripples can distort the downlink communications signals 110D and the uplink communications signals 110U, it may be desirable to minimize the ripples without increasing the orders of the bandpass filters.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.